feat(P5): IHF Phase 5 complete — agent-assisted distillation

Adds bounded AI support to the IHF governance loop. All AI outputs are
attributed (model_ref), reviewable (AgentReviewRecord), and reversible.
No autonomous decisions; no silent requirement promotion.

- T01: Schema — agent_proposals, agent_review_records,
  confidence_annotations (migration 1743379200)
- T02: AgentProposalsController (index/show/accept/reject, idempotent
  review guard), global nav "Agent" link
- T03: SummarizeClusterAction — Claude API cluster summary on widget show
- T04: DraftRequirementAction — AI requirement draft; acceptance creates
  RequirementCandidate (human-gated)
- T05: DetectDuplicatesAction — duplicate_flag proposal on candidate show
- T06: DetectPolicySensitivityAction — policy_flag with
  ConfidenceAnnotations per concern scope
- T07: ProposeImplementationAction — impl_proposal from decision show
- T08: AgentAuditDashboardAction — autoRefresh; KPI row, unreviewed queue,
  recent proposals, attribution log matrix
- T09: integration tests, SCOPE.md updated, phase5-summary.md, flake.nix
  adds http-conduit/aeson/string-conversions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Application/Schema.sql

@@ -263,3 +263,52 @@ CREATE TABLE change_evaluations (
 );
 
 CREATE INDEX change_evaluations_deployment_id_idx ON change_evaluations (deployment_id);
+
+-- Agent proposals — AI-generated outputs awaiting human review (Phase 5)
+CREATE TABLE agent_proposals (
+    id UUID DEFAULT uuid_generate_v4() PRIMARY KEY NOT NULL,
+    proposal_type TEXT NOT NULL,
+    -- proposal_type values: summary | requirement_draft | duplicate_flag |
+    --                        policy_flag | impl_proposal
+    source_widget_id    UUID REFERENCES widgets(id) ON DELETE SET NULL,
+    source_candidate_id UUID REFERENCES requirement_candidates(id) ON DELETE SET NULL,
+    source_thread_id    UUID REFERENCES annotation_threads(id) ON DELETE SET NULL,
+    source_decision_id  UUID REFERENCES decision_records(id) ON DELETE SET NULL,
+    content   TEXT NOT NULL,
+    model_ref TEXT NOT NULL,
+    confidence NUMERIC CHECK (confidence BETWEEN 0 AND 1),
+    status TEXT NOT NULL DEFAULT 'pending',
+    -- status values: pending | accepted | rejected | superseded
+    created_at TIMESTAMP WITH TIME ZONE DEFAULT now() NOT NULL
+);
+
+CREATE INDEX agent_proposals_proposal_type_idx ON agent_proposals (proposal_type);
+CREATE INDEX agent_proposals_status_idx ON agent_proposals (status);
+CREATE INDEX agent_proposals_source_widget_id_idx ON agent_proposals (source_widget_id);
+CREATE INDEX agent_proposals_created_at_idx ON agent_proposals (created_at DESC);
+
+-- One review record per proposal (human decision on AI output) (Phase 5)
+CREATE TABLE agent_review_records (
+    id UUID DEFAULT uuid_generate_v4() PRIMARY KEY NOT NULL,
+    proposal_id UUID NOT NULL REFERENCES agent_proposals(id) ON DELETE CASCADE,
+    reviewer_id UUID REFERENCES users(id),
+    decision TEXT NOT NULL,  -- accepted | rejected | modified
+    notes TEXT,
+    reviewed_at TIMESTAMP WITH TIME ZONE DEFAULT now() NOT NULL,
+    UNIQUE (proposal_id)
+);
+
+CREATE INDEX agent_review_records_proposal_id_idx ON agent_review_records (proposal_id);
+
+-- Confidence annotations — per-dimension breakdown of AI confidence (Phase 5)
+CREATE TABLE confidence_annotations (
+    id UUID DEFAULT uuid_generate_v4() PRIMARY KEY NOT NULL,
+    proposal_id UUID NOT NULL REFERENCES agent_proposals(id) ON DELETE CASCADE,
+    dimension TEXT NOT NULL,
+    -- dimension values: accuracy | relevance | completeness | policy_alignment
+    score NUMERIC NOT NULL CHECK (score BETWEEN 0 AND 1),
+    explanation TEXT,
+    created_at TIMESTAMP WITH TIME ZONE DEFAULT now() NOT NULL
+);
+
+CREATE INDEX confidence_annotations_proposal_id_idx ON confidence_annotations (proposal_id);